(1) Field of the Invention
This invention is directed to a device and method for transport of a liquid drop through an ingress aperture, e.g., into a transport zone prior to processing of the liquid. In a preferred embodiment, such aperture cooperates with opposed surfaces located within the device which provide for capillary flow of liquid within a transport zone. One of the surfaces can include a reagent-containing layer suitable for a radiometric analysis of the liquid.
(2) State of the Prior Art
A number of liquid transport devices rely upon capillary flow of liquid between two spaced-apart surfaces to spread the liquid. For example, an enclosed capillary chamber can be provided by sealing a cover sheet, e.g., around its perimeter to a reagent layer laminated to a support so that the cover sheet is left spaced away from the reagent layer a distance suitable for capillary flow. At least two apertures are then provided in the chamber. One aperture provides for the introduction of drops of liquid, and the other for the venting of air as the capillary chamber is filled. Such a device is shown, e.g., in U.S. Pat. No. 3,690,836, issued on Sept. 12, 1972.
Prior to this invention, the ingress aperture for introduction of liquid into a device of the type described above has featured a smooth, curved sidewall, such as a cylindrical wall. Such apertures suffer the disadvantage that a drop of liquid that is not accurately placed on the cover sheet, i.e., is placed with its center outside the sidewall of the aperture, tends to stay outside the aperture rather than move into it. It is only when the center of the drop is deposited well within the aperture that the surface tension of the liquid drop forces the drop into the aperture in full contact with the sidewall. Particularly this has been a problem for cover sheets formed from materials that tend to be hydrophobic, i.e., that form with the liquid in question a liquid-vapor contact angle that is greater than 90.degree.. For example, certain plastics are sufficiently hydrophobic that drops of liquid such as blood serum are more likely to remain on the cover sheet than to flow into a cylindrical aperture in the sheet.
(3) Related Applications
U.S. application Ser. No. 059,816 filed on July 23, 1979, entitled Electrode-Containing Device With Capillary Transport Between Electrodes discloses liquid transport devices that function as a bridge between two electrodes, the liquid access apertures in one embodiment being a hexagon. U.S. application Ser. No. 954,689, filed on Oct. 25, 1978, entitled "Liquid Transport Device and Method," discloses such a hexagonal aperture for use in a liquid transport device in general.